1. Technical Field
The present invention relates to a method of driving a liquid crystal panel, a liquid crystal device and an electronic apparatus to prevent malfunctions caused by the disorder of a display grayscale level in a low temperature region.
2. Background Art
In general, a passive matrix liquid crystal panel has the following construction. That is, a passive matrix liquid crystal panel interposes a liquid crystal layer between a pair of substrates having a constant gap, and a plurality of signal electrodes (segment electrodes) are formed in the shape of stripes on the side of one of the substrates facing the other substrate, and a plurality of scanning electrodes (common electrodes) are formed in the shape of stripes on the side of the other substrate facing the first substrate and are perpendicular to the signal electrodes. An optical characteristic of a liquid crystal layer interposed between both electrodes varies corresponding to the voltage difference applied to the electrodes. By this construction, an intersection of a signal electrode and a scanning electrode functions as a pixel.
While one scanning electrode is chosen, and a selected voltage is applied to the chosen scanning electrode, it is possible to control a voltage effective value applied to a liquid crystal layer of each pixel by means of applying the pulse width modulated signal to a signal electrode to distribute the off-state voltage of the same polarity as a selected voltage and the on-state voltage of opposite polarity at the corresponding ratio to display the contents of a pixel located at an intersection of a selected scanning electrode and the signal electrode. As a result, it is possible to display an objective picture with the grayscale level. In addition, because a voltage applied to a liquid crystal layer is a voltage difference of a signal applied to a signal and a scanning electrode, the voltage difference is the substantial driving signal.
However, to make the driving signal be pulse width modulated corresponding to the grayscale level in a low temperature region, a phenomenon occurs in that the predetermined order of the grayscale level is not maintained (grayscale level turning over), and hence, this causes decreased display integrity, which is considered as a weak point.
As an exemplary technology to prevent grayscale level turning over in such a low temperature region, it has been known that the relationship between the pulse width of the driving signal to be applied to a liquid crystal and the temperature of a liquid crystal panel are given as shown in FIG. 19 (for example, refer to Japanese Unexamined Patent Application Publication No. 2001-159753 (refer to FIGS. 1 and 9, and 0032 paragraph)). As a result, according to this technology, a pulse width opposed to each grayscale level is respectively changed depending on the temperature in a low temperature region. Because frequency components of driving signals applied to a liquid crystal layer at the time of the brightest grayscale level (white) and the darkest grayscale level (black) are raised (described below in detail), and grayscale level turning over in a low temperature region is prevented. When a pulse width corresponding to a grayscale level is required, a table created in advance that has stored the relationship of both is used.
However, in using the above technology, it is necessary not only to prepare at least two patterns as a table for the use of normal temperature and low temperature, but also to compensate by gradually changing a pulse width corresponding to each grayscale level from the maximum value to the minimum value in a low temperature region. Because of this, the technology causes a problem in that a construction to prevent grayscale level turning over becomes complicated. Further, a complexity of the construction directly increases power consumption, which conflicts with the trend of low power consumption required in the field where a liquid crystal panel is used.
The present invention is designed considering the above circumstances, and a purpose is to provide a method of driving a liquid crystal panel, a liquid crystal device and an electronic apparatus that can prevent the disorder of the grayscale level in a low temperature region by means of a simple construction.